The Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite is the engine for the Internet and networks worldwide. Its simplicity and power has led to its becoming the single network protocol of choice in the world today. The architectural model of TCP/IP protocol suite is named for two of its important protocols which are Transmission Control Protocol (TCP) and Internet Protocol (IP).
The main design objective of TCP/IP is to build an interconnection of networks referred to as an internetwork or internet that provides universal communication services over heterogeneous physical networks.
The TCP/IP Protocol Layers
It is built around the TCP/IP protocol suite. A protocol suite is a large number of related protocols that work together to allow networked computers to communicate. Layers with the same names as Open Systems Interconnection (OSI) Model don’t functions exactly the same.
The application layer is provided by the program that uses TCP/IP for communication. An application is a user process cooperating with another process usually on a different. Examples of applications include Telnet and the File Transfer Protocol (FTP). The interface between the application and transport layers is defined by port numbers and sockets.
The transport layer provides the end-to-end data transfer by delivering data from an application to its remote peer. Multiple applications can be supported simultaneously. The most-used transport layer protocol is the Transmission Control Protocol (TCP), which provides connection-oriented reliable data delivery, duplicate data suppression, congestion control and flow control. Another transport layer protocol is the User Datagram Protocol (UDP). It provides connectionless, unreliable, best-effort service. As a result, applications using UDP as the transport protocol have to provide their own end-to-end integrity, flow control, and congestion control, if desired. Usually, UDP is used by applications that need a fast transport mechanism and can tolerate the loss of some data.
The internetwork layer, also called the internet layer or the network layer, provides the “virtual network” image of an internet. Internet Protocol (IP) is the most important protocol in this layer. It is a connectionless protocol that does not assume reliability from lower layers. IP does not provide reliability, flow control, or error recovery. These functions must be provided at a higher level. IP provides a routing function that attempts to deliver transmitted messages to their destination. A message unit in an IP network is called an IP datagram. This is the basic unit of information transmitted across TCP/IP networks. Other internetwork-layer protocols are IP, ICMP, IGMP, ARP, and RARP.
Network Interface Layer
The network interface layer, also called the link layer or the data-link layer, is the interface to the actual network hardware. This interface may or may not provide reliable delivery and may be packet or stream oriented. In fact, TCP/IP does not specify any protocol here, but can use almost any network interface available, which illustrates the flexibility of the IP layer. Examples are IEEE 802.2, X.25 (which is reliable in itself), ATM, FDDI and even SNA. TCP/IP specifications do not describe or standardize any network-layer protocols per se; they only standardize ways of accessing those protocols from the internetwork layer.